The present disclosure relates to an implant, such as a cranial implant, for attachment to an edge of a defect in a bone structure, the implant comprising a direction of extension at or near the rim extending substantially perpendicular to the rim wherein the rim is configured to be attached to the edge of the bone structure.
Such implants, which are sometimes referred to as patient specific implants (PSI), are employed for repairing defects in bone structures resulting from e.g. surgery or trauma and/or a birth defect. An implant partially or fully closes a defect, such an opening in a skull, protects the tissue underneath, e.g. brain tissue, and/or corrects and/or restores the contour of the bone structure. Such implants are generally custom made, preferably adhering to the ISO 13485 quality management standard for medical devices.
Implants may have different origins. For instance, autogenous grafts are taken from one part of a human or animal body and implanted in another part of that same body and allografts are bone grafts taken from an individual from a species and inserted in the body of another individual of that same species. Alloplastic implants are implants made from body foreign material.
All implants have in common that they must be securely fixed to the bone structure. Implant migration and micro-movements may hinder osteointegration (sometimes also referred to as osseointegration) and even result in rejection of the implant. Implant fixation is generally done by suturing or screwing the implant to the bone structure via holes, which are provided into or through the implant and/or the bone structure.
U.S. Pat. No. 6,618,623 discloses a ferrule for retaining an implantable device within a cranial opening of a patient. The ferrule is inserted into the cranial opening and fixed to the cranium. Then an implantable device is inserted into the ferrule and secured thereto. The ferrule may comprise an intra-osseous extension and is secured to the patient's cranium with (self-tapping) bone screws.
EP 2 014 258 by the present inventors pertains to an implant, such as a cranial implant, comprising a rim and one or more fasteners for attaching the rim to an edge of a defect in a bone structure. One side of the rim is broader than the other side of the rim and/or comprises one or more protrusions extending beyond the periphery of the other side of the rim, such that, upon placing the implant in the defect, the rim and/or protrusions rest(s) on the edge of the defect. The fastener(s) is/are mounted or mountable in or on at least the rim and comprise(s) at least one element which is extendible in a direction away from the rim to grip underneath the bone structure. The fasteners of the implant of EP 2 014 258 are accommodated in clip mounts or guides configured such that a portion of the fastener is extendible in a direction extending away from the rim at an angle which is at most acute with respect to the direction of extension of the implant, so as to be extendible underneath the bone structure.
U.S. Pat. No. 6,197,030 discloses elastic-loaded retractable shank surgical pins having a hollow shank adapted to receive an elastic-loaded retractable shank which can be inserted into a bone flap or into the walls of a skull cavity from which the bone flap has been removed, when the retractable shank is compressed against the elastic loading, and the bone flap is placed into position in the skull cavity. The retractable shanks are allowed to expand outwards into corresponding holes positioned in the skull or bone flap, securing the latter in place without the necessity of protruding wires or other conventional locating devices. The pins need not be positioned parallel to each other, and may be spaced around the bone flap, preferably constituting the sole means of securing the bone flap in the skull cavity. However, such pin type devices are relatively complex and therefore expensive and delicate devices, in particular relative to a screw. Such pin type devices also do not allow removal of the bone flap once implanted, e.g. in case of complications. Relying on elastic loading, the pins cause compressive forces onto the skull and/or the bone flap which cannot be determined and/or controlled accurately and micro-movements of the pin and/or the bone flap with respect to the skull are inherent.
Bone screws, tacks and the like are proven techniques but necessitate intrusion into the bone structure and, once applied, exert (lateral) compressive forces on the bone structure. Compressive forces in turn may cause resorption of bone and loosening of the fixing means. Micro-movements due to play between different parts of the implant or the fixing means or between the fixing means and the bone structure and/or implant may increase damage and loosening and should be prevented. A balance should thus be found between minimum compressive forces and optimum fixation. Further, the implant and its fixation means form an invasive volume inside the patient's body. Such volume should be minimal, in particular for a cranial implant to prevent damage to the brain.